It has long been known to incorporate various elastomers such as block copolymers, sequenced or otherwise, of the conjugated diene/vinylaromatic type and most often block copolymers such as styrene/butadiene/styrene di-blocks, into bitumens, in order to improve their mechanical properties and to satisfy the standards established for use as binders. With vulcanization, products are obtained which retain their elastic characteristics, even at low temperatures
However, the production of such bitumen/polymer mixtures causes problems relating to their homogeneity and to the very long malaxation time needed for obtaining the appropriate homogeneity. For example, even under the most favorable conditions known to date, the mixtures must be kept stirred for at least two hours, and most often three to four hours, at a temperature on the order of 150-190C., in order to achieve correct homogeneity of the bitumen/polymer mixture before the vulcanizing agent is added.
Thus, the bitumen/rubber compositions of the prior art were difficult to use, and had poor properties of cohesion and very poor resistance to cracking.
In addition, in the prior processes, elemental sulphur is used as a vulcanizing agent. With elemental sulphur, the vulcanization reaction is very rapid and uncontrollable and, more often than not, an unusable gel is produced.
In order to remedy some of these disadvantages, it has been proposed to mix the rubber with a petroleum cut to incorporate it more rapidly into the bitumen. However, it was found that during the evaporation of this petroleum cut, the final product had a low resistance to cracking due to a lack of elasticity.
The present invention relates to a process for preparing bitumen/polymer compositions having improved properties, including improved resistance to cracking and higher elasticity.
One object of the present invention is to provide a process for preparing bitumen/polymer compositions in the presence of novel vulcanizing agents, in order to achieve better control of the vulcanization reaction.
Another object of the invention is to provide a process for preparing bitumen/polymer compositions which does not necessitate the incorporation of a petroleum cut.